Process for producing mixed cellulose esters



Patented Dec. 19, 1950 PROCESS FOR PRODUCING MIXED CELLULOSE ESTERSGeorge Alvin Richter, Jr., Springfield, Pa., as- ,signor to AmericanViscose Corporation, Wilmington, Del a corporation of Delaware NoDrawing.

Application February 21, 1948,

Serial No. 10,173

Claims.

This invention relates to modified cellulose estors and moreparticularly to cellulose esters containing chemically bound radicalsderived from agents which are capable of reacting bifunctionally withcellulose.

This application is a continuation of my pending application Serial No,526,812, filed March 16, 1944, now abandoned.

Cellulose fibers have an extremely high degree of plasticity which isaccompanied by low elasticity, and tend to undergo irreversible flowunder moderate stresses. Products molded from cellulose or itsderivatives, such as cellulose esters, exhibit the same properties andtend to become deformed under stress, and this tendency is not reversedand the products do not revert to their original form when the stress isremoved.

I have now prepared a series of modified cellulose esters which alsocontain chemically bound radicals derived from agents which are capableof reacting bifunctionally with cellulose, the properties of which areradically different from those of cellulose or unmodified estersthereof, in

' that in the new products the high degree of plasticity which is adistinguishing characteristic of cellulose or cellulose esters ismodified in favor of a greatly enhanced elasticity.

The esters preferably contain from about one or less than one radicalderived from the agent capable of reacting bifuncticnally with celluloseper about 20 anhydroglucose. units to one or less than one such radicalper 500 anhydroglucose units or more. Of course, the ratio of themodifying radicals to glucose units may vary, but where the ratio issubstantially higher than one in, 20, the resulting product is extremelyrigid and non-plastic.

In accordance with the invention, the radicals derived from agentscapable of reacting bifunc" tionally with cellulose may be introducedsimultaneously with or, in some cases, prior to the production of theesters.

According to one embodiment of the invention, at least one monobasicorganic acid radical and at least one polybasic organic acid radical areintroduced simultaneously into cellulose by reaction thereof with amonofunctional esterifying reagent and an esterifying agent capable ofreacting bifunctionally with cellulose, the reaction being carried outin the presence of a substance in which the reaction product is at leastpartially solvated, that is, dissolved or swollen as it is formed duringthe reaction.

. Suitable monofunctional reagents are monobasic or anic. acids. such asce ic. propionic.

butyric, lauric acids, etc., anhydrides of such acids, and acid halidesderived therefrom.

Suitable bifunctionally reacting agents are such polybasic organic acidsas adipic, succinic, sebacic acids, etc., as well as polyhalides of suchacids.

Diacids derived from glycol, as well as dihalides thereof, such ascompounds having the general formula XOCCH2CH2 (OCH2CH2) nCH2CH2COXwhere X is hydroxyl or halogen and n is any integer but preferably from1 to 4, inclusive, may also be used. Such diacids derived from glycolmay be prepared by the general procedure described by Bruson, JournalAmerican Chemical Society 64, pages 2457 and 2850.

In accordance with the invention, cellulose is simultaneously reactedwith at least one polybasic organic acid, and at least one anhydride ofa monobasic organic acid capable of esterilying cellulose, in thepresence of a catalyst, which may be a mineral acid catalyst, forexample, and a substance in which the reaction product is dissolved orswollen during the reaction. Alternatively, the cellulose may besimultaneously reacted with at least one monobasic organic acid, and atleast one polybasic organic acid, in the presence of an impeller whichmay be an anhydride of a halogen-substituted monobasic organic acid, acatalyst, and a substance in which the reaction product is dissolved orswollen during the reaction.

Acid halides may also be used. Thus, the cellulose may be reactedsimultaneously with at least one monobasic organic acid halide, and atleast one polybasic organic acid halide, in the presence of a condensingagent which is inert with respect to the halides, such as an organicbase as, for instance, the tertiary amines, pyridine, quinoline,n-methyl morpholine, etc., in the presence of a solvent or swellingagent for the reaction product.

According to another embodiment of the invention, introduction of thepolybasic organic acid radicals may be effected, in some cases, prior toesterification of the cellulose with a monobasic organic acid. Thus,cellulose may be reacted with one or more diacids derived from glycol,or dihalides of such acids, in the presence of a condensing agent orcatalyst, and the product thus obtained may then be subsequently reactedwith at least one monobasic organic acid, in the usual manner.

An important feature of the invention. is that reaction is carried outin the presence of a substance in which the reaction product isdissolved or swollen as it is formed during the course of the reaction,which results in the reaction mass being maintained in a highly swollenor dissolved state and thus insures substantially uniform reactionbetween the cellulose and the monofunctional and bifunctional reagents.Such substances are, for example, toluene, dioxane, acetone, eto. Thefinal products which may be obtained by precipitating the reaction massfrom water, may be soluble or substantially insoluble in suchsubstances.

The amount of monofunctional reagent used may vary, but in general Iprefer to use an amount thereof sufiicient to form a tri-ester. If amore lowly esterified final product is desired, such as a secondary ormono-ester, the tri-ester may be suitably hydrolyzed by conventionalmethods, after completion of the reaction with the bifunctionallreacting esterification agent. By the choice of bifunctionalesterification agent and the amount thereof participating in thereaction, it is possible to selectively adjust certain physicalproperties of the final products, such as solubilities and softeningtemperatures. Although in all cases the modified esters show a lesserdegree of plasticity and a greater degree of elasticity, and in generalmuch higher softening and melting temperatures andresistance to commonsolvents, as compared with corresponding cellulose esters which do notcontain the modifying groups, modified esters may also be obtained whichdo not greatly differ from the un modified esters in respect ofsolubility and soitening temperatures. The degree to which the finalmodified esters are soluble in substances which are solvents forcellulose esters, such as acetone, dioxane toluene, etc., for instance,may vary, depending upon the amount of bifunctional esterification agentused, greater amounts decreasing the solubility and lesser amountsincreasing it. Thus, final products may be ob tained which form smoothrelatively clear solutions in solvents such as acetone, toluene,dioxane, etc., or which form extremely viscous gellike masses therein.Also, final products may be obtained which are insoluble in such commonso1- vents or which are merely swollen slightly when added thereto.Generally speaking, the modified esters do not have melting points belowdecom position temperatures or sharp softening points, are substantiallunaffected at temperatures at which the unmodified esters melt orsoften, do not show a tendency to soften except Within high temperatureranges, and at temperatures above the softening range are less plasticand more rubber-like than unmodified esters. However, the softeningtemperature in some instances may be varied, depending upon the amountand type of bifunctional esterification agent used, the tendency tosoften at relatively low temperatures being more marked in those caseswhere such agent is used in relatively small amounts and has a longerchain as compared to the ester side chain derived from the monobasicacid. The use of marginal amounts of the bifunctional esterificationagent in the reaction thus permits a sensitive adjustment of thesolubility and softening characteristics of the end product. The amountof such agent to be used depends upon the properties desired in thefinal products. In general to achieve the objectives of this inven tionit is desirable to use the bifunctionally reacting agent, such as thedihalide of an organic 4 dibasic acid, in amounts varying from l l0 toabout 4 10 mols thereof per 5 gms. of cellulose, the final productcontaining, usually, one or less than one dibasic acid radical per 20anhydroglucose units, to one or less than one dibasic acid radical per500 anhydroglucose units, or more.

The products are obtained in the form of fibrous masses Which are, forthe most part, insoluble, infusible, and heat-insensitive, but which incertain cases, as previously indicated, ma be soluble to varying extentsand more Or less susceptible to softening by heat.

Some of the insoluble or substantially insoluble modified esters, suchas cellulose butyrate containing sebacic acid radicals may be molded bycompression and injection molding techniques to give molded articleswhich are characterized by hardness, resistance to cold flow, andresistance to flow at elevated temperatures. The molded products mayundergo some flow under stress but due to their quality of rapid andsubstantially complete elastic recovery, show a lively return to theiroriginal form upon the removal of stress.

Those products which are soluble in solvents such as acetone, forexample, may be dissolved therein and extruded through a spinneret orthe like into an evapcrative atmosphere, in accordance with thedry-spinning process, to form artificial filaments, or may be cast fromsuch solutions to give films, sheets, coatings etc. which are durableand stable. 7

If desired, substances may be added to the products to give variouseffects. Some of the substances which may be added are suitable coloringmaterials, such as dyes, pigments, particles of colored materials togive mottled efiects, metallic particles or the like.

The products exhibit properties such as a lesser degree of plasticity,greatly increased elasticity, generally increased softening and meltingtern perature ranges, and range of solubility in common solvents whichare distinctly different from the properties of corresponding celluloseesters, such as cellulose laurate, cellulose propionate, etc., which donot contain the chemically combined modifying polybasic acid radicals.While the reasons for the marked change in properties cannot be statedprecisely, it is believed that the change may be predicated upon achemical reaction of the polybasic acids or their halides with hydroxylgroups on parallel cellulose chains, so that cross-links are formedbetween the primary valence chains of 'the cellulose derivatives.

As previously indicated, the introduction of the radical or radicalsderived from the hifunctional esterification agent may be efiectedsimultaneously with, or in ornc instances, prior to substantial ester cfthe cellulose with the monobasic acids or haiides, when the reaction iscarried out 111 the presence of a solvent capable of swell ng ordissolving the reaction product as it is during the reaction. However,it has not n found practicable to effect chemical combination. or thepolybasic acid radicals in the case of pre-shaped cellulose esters, andthe more highly esterifiej the starting material the greater is thedifficulty encountered.

It appears that 1 olyiunctional es'terification agents, such as l-alides of polybasic acids, react chel the free hydroxyls of previouslysh ly esterified cellulose, only with considerable difiiculty, at all,and that in all cases Where shaped masses, fibers or the like consistingof or comprisin partially esterified cellulose have been treated withpolybasic acids or their polyhalides in the absence of an agent which iscapable of dissolving or swelling the reaction product as it is formed,only superficial or surface effects have been obtained.

The invention will be further illustrated by the following example inwhich the quantities are stated in parts by weight.

Example About 10 parts of cotton linters were treated with a mixture of0.5 part of sebacic acid dissolved in 50 parts of glacial acetic acidfor 2 hours at 38-45 C. after which 11.5 parts of glacial acetic acidand 0.02 part of sulfuric acid were added. The temperature wasmaintained at about 38-45 C. for 1 hours, and then permitted to drop to30 C., and maintained there for 1%, hours. The mass was cooled to 18 C.About 25.7 parts of acetic acid anhydride cooled to C. were added. Themass was then cooled to C., and a mixture of 0.33 part of sulfuric acidand 0.57 part of glacial acetic acid was stirred into the mass, and themixture was kept at 25 C. for about 3 hours. A very fibrous white masswas thus obtained. A

mixture of 7 parts of sulfuric acid and 7 parts of glacial acetic acidwas added, to hydrolyze the product to a secondary acetate. Thehydrolyzed material was placed in a water bath at 40 C. for 24 hours.The mass was thinned with a little acetone and precipitated by stirringin water; the precipitate was washed and dried. The Product did not havea melting point below decomposition; had a softening range of about230-235 C., and was insoluble in acetone.

.The above examples and description are given by way of illustration,and modifications or variations may be made therein without departingfrom the spirit and scope of the invention as defined in the claims.

I claim:

1. A process for making modified cellulose esters containing monobasicacid radicals, and

dibasic acid radicals which form cross-links between cellulose chains,which comprises reacting unesterified cellulose simultaneously with ananhydride of an unsubstituted, saturated, lower aliphatic monobasic acidin an amount sufiicient to produce a tri-ester, and with anunsubstituted aliphatic dibasic acid in an amount equal to from 4x10- to4x10- mols per each five grams of cellulose, in the presence of amineral acid as an esterification catalyst, and of an inert diluentwhich is an at least partial solvent for the reaction product, thereaction being effected in the absence of an organic base and of waterin excess of the amount of moisture normally retained by the cellulose,hydrolyzing the product to a secondary monobasic acid ester containingthe dibasic acid radicals forming cross-links between the cellulosechains, and separating the hydrolysis product.

2. A process as in claim 1, wherein the cellulose is simultaneouslyreacted upon with acetic acid anhydride and sebacic acid.

3. A process as in claim 1, wherein the catalyst is sulfuric acid.

4. A process as in claim 1, wherein the inert diluent is glacial aceticacid.

5. A process as in claim 1, wherein the cellulose is simultaneouslyreacted upon with acetic acid anhydride and sebacic acid, in thepresence of sulfuric acid and glacial acetic acid.

GEORGE ALVIN RICHTER, JR.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,093,464 Mahn Sept. 21, 19372,183,982 Blanchard et al. Dec. 19, 1939 2,245,208 Malm et a1 June 10,1941 2,358,387 Dreyfus Sept. 19, 1944 2,380,896 Kaszuba July 31, 1945

1. A PROCESS FOR MAKING MODIFIED CELLULOSE ESTERS CONTAINING MONOBASICACID RADICALS, AND DIBASIC ACID RADICALS WHICH FORM CROSS-LINKS BETWEENCELLULOSE CHAINS, WHICH COMPRISES REACTING UNESTERIFIED CELLULOSESIMULTANEOUSLY WITH AN ANHYDRIDE OF AN UNSUBSTITUTED, SATURATED, LOWERALIPHATIC MONOBASIC ACID IN AN AMOUNT SUFFICIENT TO PRODUCE A TRI-ESTER,AND WITH AN UNSUBSTITUTED ALIPHATIC DIBASIC ACID IN AN AMOUNT EQUAL TOFROM 4X10**-5 TO 4X10**-4 MOLS PER EACH FIVE GRAMS OF CELLULOSE, IN THEPRESENCE OF A MINERAL ACID AS AN ESTERIFICATION CATALYST, AND OF ANINERT DILUENT WHICH IS AN AT LEAST PARTIAL SOLVENT FOR THE REACTIONPRODUCT, THE REACTION BEING EFFECTED IN THE ABSENCE OF AN ORGANIC BASEAND OF WATER IN EXCESS OF THE AMOUNT OF MOISTURE NORMALLY RETAINED BYTHE CELLULOSE, HYDROLYZING THE PRODUCT TO A SECONDARY MONOBASIC ACIDESTER CONTAINING THE DIBASIC ACID RADICALS FORMING CROSS-LINKS BETWEENTHE CELLULOSE CHAINS, AND SEPARATING THE HYDROLYSIS PRODUCT.